Abstract The polarized infrared and Raman spectra of caesium hydrogen succinate monohydrate single crystal have been measured. The results obtained are discussed on the basis of the crystal structure and selection rules. The antisymmetric stretching vibration, ν aOHO, of the strong hydrogen bond gives rise to a very intense absorption in ac face spectra, being strongest in the Z direction. For this vibration, correlation field splitting was not observed. The out-of-plane deformation vibration, γOHO, obeys the selection rules for the factor group. The hydrogen bond has an appreciable influence on the νCO vibration, giving rise to an anomalous band shape. The twisting motion of the H 2O molecule appears as an intense and broad band, contrary to a previous literature assignment.